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 Post subject: Shorting issue in B+ Zenith H-845
PostPosted: Feb Tue 06, 2018 5:18 pm 
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Location: alameda,CA
I'm having the damnedest time on a model of Zenith I've probably restored at least 10 times over. Its one of those large Zenith high fidelity AM/FM sets. In fact here is one of those that I restored:
http://www.californiahistoricalradio.co ... rticle.pdf

I bought one on Saturday. At the time it worked. Upon getting it home I did as I usually do and recapped it. Nothing out of the ordinary and by now I've almost memorized the chassis. BUT... For whatever reason of which I cannot figure out I am not getting any B+ on three of the four electrolytics. I get 67 volts on the 80uF section and nothing on the others that are all 40uF. I replaced the selenium rectifier with a diode and resistor as usual. Now when the set is turned on I get a slight hum from the speaker and the new resistor paired with the diode gets really hot as does a 270 ohm resistor that ties into the output transformer. So there's a short in there somewhere.

I have checked everything over and over. Removed and checked all of the tubes for shorts, tested all of the resistors in the B+ supply, re-checked my work as far as what capacitor goes where and so on. Its really befuddling to me so if anyone has some ideas that would be great.


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 Post subject: Re: Shorting issue in B+ Zenith H-845
PostPosted: Feb Tue 06, 2018 5:21 pm 
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Location: Detroit, MI USA
With the power off, read the resistance to ground from the first electrolytic section which has no voltage and report back.

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Dennis

Experience is what you gain when the results aren't what you were expecting.


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 Post subject: Re: Shorting issue in B+ Zenith H-845
PostPosted: Feb Tue 06, 2018 5:50 pm 
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Will do after work this evening...


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 Post subject: Re: Shorting issue in B+ Zenith H-845
PostPosted: Feb Wed 07, 2018 2:14 am 
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Food for thought....

Questionable Zenith capacitors if so equipped...

/viewtopic.php?f=19&t=309923


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 Post subject: Re: Shorting issue in B+ Zenith H-845
PostPosted: Feb Wed 07, 2018 5:07 am 
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The issue was weird. There is a 24 ohm resistor that comes
Off of the rectifier. It tested good with my meter but in reality was shorted. Maybe applied current tripped it to short. Oh well. It works now!


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 Post subject: Re: Shorting issue in B+ Zenith H-845
PostPosted: Feb Wed 07, 2018 6:14 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: North of Mpls, Minnesota
A shorted surge resistor coming of the rectifier won't cause a loss of B+, there is something else going on.

Dave


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 Post subject: Re: Shorting issue in B+ Zenith H-845
PostPosted: Feb Wed 07, 2018 3:20 pm 
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Well... whatever it was that was what solved the issue and thus now it works perfectly. Hooray!


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 Post subject: Re: Shorting issue in B+ Zenith H-845
PostPosted: Feb Thu 08, 2018 10:53 am 
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You may have a "Dry Joint" that went open (not withstanding a resistor can do that & I have had a couple of "Micamold" ones do that). Dry joints are still very popular.

Marc


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